Polyester films have been expensively used in various applications because of excellent mechanical properties and processing properties thereof. In addition, laminates formed of a polyester film and a polyolefin have also been extensively used in various applications such as packaging materials because they are excellent in film strength and gas-barrier property as well as exhibit a good heat sealability, etc. In recent years, the above laminates have also been applied to automobiles and solar batteries. These laminates have been produced by the method of subjecting a polyester and a polyolefin to extrusion lamination process, or by the method of heat-sealing these materials. However, since adhesion between the polyester film and the polyolefin is poor, it is generally required to further provide an adhesive layer in order to form a laminated film formed of the polyester film and the polyolefin, which tends to induce deterioration in productivity and increase in costs. As described in Patent Documents 1 and 2, etc., there has been extensively used the method of providing an adhesion-modifying layer as an easy-bonding layer on a polyester film. However, the above method may still fail to provide a laminated polyester film having a satisfactory adhesion property to polyolefins.
Also, in Patent Document 3, there is described an aqueous coating material capable of modifying an adhesion property to polyolefins. However, the above conventional technique may also fail to improve adhesion between a polyester film and a polyolefin to a sufficient extent.